The appearance of colored patterns: pattern-color separability

We have measured how color appearance of squarewave bars varies with stimulus strength and spatial frequency. Observer's adjusted the color of an uniform patch to match the color appearance of the bars in squarewave patterns. We used low to moderate squarewave patterns, from one to eight cycles per degree (cpd). The matches are not photoreceptor matches, but rather are established at more central neural sites. The signals at the putative central sites obey several simple regularities. The cone contrast of the uniform patch is proportional to squarewave stimulus strength (colorhomogeneity) and additive with respect to the superposition of equal frequency squarewaves containing di erent colors (color-superposition). We use the asymmetric matches to derive, from rst principles, three patterncolor separable appearance pathways. The matches are explained by two spectrally opponent, spatially lowpass mechanisms and one spectrally positive, spatially bandpass mechanism. The spectral mechanisms we derive are very similar to luminance and opponent mechanisms derived using entirely di erent experimental methods.